National Bureau of Standards

Library, N.W. Bids JUL 1 7 1964

m O

Standard Reference Materials:

NBS MISC. PUBL 260-1

National Bureau of Standards

Library, . E-01 Admin. Bldg. OCT 1 1981 ISiOO'j

fO'O

.W>1

PREPARATION OF NBS

WHITE CAST IRON SPECTROCHEMICAL

STANDARDS

U.S. Department of Commerce

National Bureau of Standards
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau's activities is suggested in the following

listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics; Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere and Space Telecommunications. Radio Systems. Upper Atmosphere and Space Physics. Institute for Applied Technology. Textiles and Apparel Technology Center. Building Research.

Industrial Equipment. Information Technology. Performance Test Development. Instrumentation. Transport Systems. Office of Technical Services. Office of Weights and Measures. Office of Engineering Standards. Office of Industrial Services.

* NBS Group, Joint Institute for Laboratory Astrophysics at the University of Colorado. ** Located at Boulder, Colorado.
UNITED STATES DEPARTMENT OF COMMERCE • Luther H. Hodges, Secretary NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Standard Reference Materials:

Preparation of NBS

White Cast Iron Spectrochemical

Standards

Robert E. Michaelis and LeRoy L. Wyman

Institute for Materials Research

National Bureau of Standards Washington, D.C.

National Bureau of Standards Miscellaneous Publication 260-1

Issued June 19, 1964

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C, 20402 - Price 30 cents
Library of Congress Catalog Card Number: 64 — 60045
PREFACE

Within the framework of the NBS Institute for Materials

Research the area of standard reference materials is a broad

and important one, including the preparation, characterization

and distribution of a wide variety of materials in such diverse

fields as metallurgy, polymers and inorganic materials. In carrying out such a program there is much interaction with

representatives of industry and science, beginning with discussions as to which primary standard materials will do most

to advance technology, the furnishing of materials and fabrication of samples, and the characterization and certification

of the materials by cooperative efforts. The many groups

participating in a standards program are very interested In detailed Information on specific aspects of the program —

but to date there has been no publication outlet for such

written discussions.

To meet this need, NBS Miscellaneous Publication 260 has

been reserved for a series of papers in the general area of

"standard reference materials". This series will present the

results of studies and investigations undertaken within the

Institute for Materials Research with emphasis on the preparation and characterization of standard reference materials.

This subject-oriented series will provide a means for rapid

dissemination of this detailed information and we hope will

stimulate the use of standard reference materials in science

and industry.

iii
OTHER NBS PUBLICATIONS OF INTEREST

NBS Miscellaneous Publication 241., Standard Materials

Issued by the National Bureau of Standards: A Descriptive List with Prices, March 1962. 30 cents. NBS Miscellaneous Publication 250, Calibration and Test

Services of the National Bureau of Standards, November

1963. 70 cents. Send orders with remittance to: Superintendent of Documents, U. S. Government Printing Office, Washington,

D. C.j 20402. Remittances from foreign countries should

include an additional one -fourth of the purchase price

for postage.

iv
CONTENTS

PAGE

1. INTRODUCTION 1

2. CONSIDERATION FOR PREPARATION 3

3. TYPE OF CAST IRON FOR STANDARDS 4

4. CHEMICAL COMPOSITIONS 5 5. CASTING 9 6. MELTING 13

7. PRELIMINARY ANALYSIS 16

8. HOMOGENEITY TESTING 17

9. SAMPLE IDENTIFICATION 21

10. HEAT TREATMENT 23

11. CHEMICAL ANALYSIS 24

12. CONSISTENCY TESTING 25

13. PRECAUTIONS FOR APPLICATION 27

14 . ADDENDUM 29

15. REFERENCES 31

v
LIST OF TABLES

TABLE NO. PAGE

1. Planned Compositions of Eight Proposed

NBS White Cast Iron Spectrochemical

Standards . . . . , 7

2. Materials Used in Melting NBS White

Cast Iron Standards l4

3. Log of Melt for Brake Drum (350 lb)

Standard (NBS No. 1179) January 8 3 I960 15

4. Recovery Values for 10 Elements in the

Eight NBS White Cast Iron Standards . . . 16

5. Typical Homogeneity Test Data: Manganese,

Nickel s and Molybdenum in Brake Drum

Standard, NBS No. 1179, by X-Ray

Determinations 20

LIST OF FIGURES

FIGURE N0 o PAGE

1. Water-cooled copper mold assembly

designed and constructed at NBS

for the preparation of white cast iron spectrochemical standards .... 10

2. Schematic diagram of NBS white cast iron spectrometric samples 22

vi
PREPARATION OF NBS WHITE CAST IRON

SPECTROCHEMICAL STANDARDS

Robert E. MIchaelis and LeRoy L. Wyman

Institute for Materials Research

National Bureau of Standards

Several methods have been investigated for the

preparation of cast iron spectrochemical standards

and a satisfactory procedure has been devised.

The method involves casting the molten metal into

a grid type of mold on a massive water-cooled

copper plate. The method has been applied to the

preparation of eight NBS white cast iron spectrochemical standards containing a graded concentration range for some 20 element s, of which the

following 10 initially have been certified: C, Mn, P, S, 31, Cu, Ni v Cr^ V 3 and Mo. Details of

the planning and preparation are given with particular emphasis on the problems peculiar to standards for cast materials.

1 . INTRODUCTION

Cast iron may be described generally as an alloy of iron

and carbon where the carbon content is between 1.7 and 4.5

percent. This is more carbon than can be retained in

austenite at the eutectic temperature; hence on slow cooling

the casting normally will exhibit a matrix of pearlite with

many graphite flakes dispersed throughout. Such material is

known as gray iron and was so named because of the characteristic "gray" fracture imparted by the graphite flakes.

The tonnage production of gray iron exceeds that of all other

1
cast metals combined. Also included in the general term

"cast iron" are pig irons, white irons, chilled irons, and

malleable irons

.

The rapid methods of spectrochemical analysis have been

employed widely in the cast iron industry for the determination of most metallic constituents. In recent years,

however, developments in spectrochemical instrumentation,

particularly the vacuum emission spectrometer, made possible

the complete analysis of cast irons including determinations

for carbon, phosphorus, and sulfur. This markedly extended

the use of spectrochemical analysis in the cast iron field.

Also of significant interest has been the increasing application of x-ray spectrochemical methods for the analysis of

materials such as cast iron.

The major limitation to quantitative spectrochemical

analysis is that the methods are not absolute, but are dependent on the technique of comparison with samples of

known composition, referred to as standard samples. Thus the

problem of calibration is of paramount importance to the

accuracy of spectrochemical analysis. Standard samples must

not only be of high homogeneity and have accurate values

assigned to them, but also extreme caution must be exercised

in matching the standards and the unknown samples with respect

to all variables such as size, shape, composition, and

metallurgical condition.

The acute need by both industry and government for

2
reliable and accurate cast iron spectrochemical standards

was made clear to the National Bureau of Standards in the

early 1950 1 s by surveys and communications; and in 1955 an active program for the preparation of suitable standards was initiated

.

The main purposes of this paper are to describe the

development of a satisfactory method of preparation for cast

iron standards and to evaluate the application of this method

to a set of eight prepared NBS spectrochemical standards.

This work was supported in part by the American Iron and

Steel Institute.

2. CONSIDERATION FOR PREPARATION

The preparation of spectrochemical standard samples to be provided in the "as cast" condition presents several

difficulties not encountered in those which can be provided

in the wrought condition. For wrought standards s non- homogeneous portions can be determined and discarded prior

to working to the final size. Equally significant is the

fact that the final homogeneity in the wrought standard can

be improved markedly over that of the selected material by

appropriate working and heat-treating operations [l]. For

"as cast" standards,, the required chemical homogeneity and

desired metallurgical structure are obtained solely through

metal pouring and casting procedures.

Additional difficulties in the preparation of cast iron

standards over most other cast materials are encountered

730-267 0-64 —2 3
because of the variety of complex metallurgical structures

which may be formed on the solidification of the cast iron

from the molten state, and which may markedly influence the

spectrochemical results. The final metallurgical structure

depends primarily on the composition, pouring temperature,

and rate of cooling.

3. TYPE OF CAST IRON FOR STANDARDS

Since gray iron is by far the most widely used type of cast iron, it commanded initial consideration. On investigation at NBS and elsewhere, however, it was shown that the

graphite flakes, in terms of amount, size, shape, and

distribution, had a pronounced effect on the volatility rates

in the determination of some elements by optical emission

analysis

.

In white cast iron virtually all of the carbon exists

in the combined form and there is essentially no free

graphite. Although limited in engineering applications, the

white cast iron was considered to be the most advantageous

material for the spectrochemical standards for the following

reasons. (1) It would provide a uniform metallurgical

structure for a series of standards to cover wide concentration

ranges for the elements of interest. (2) It would offer a casting material that could be prepared to provide the

requisite homogeneity of chemical composition. (3) Investigation had shown that test samples with an induced white

structure could be prepared in the foundry for most types of
iron; these could thus be analyzed directly relative to the

white iron standards. The white structure can be induced in

at least a portion of the test samples either by using a rapid

chill-casting procedure or by making certain additions known

to promote whiteness, such as tellurium or bismuth, or by a combination of both, to the test ladle or mold. (4) Finally,

the white cast iron provides the opportunity to make the

important determination of total carbon by vacuum optical

emission analysis, which would not be possible if much of

the carbon was present in an uncombined form.

4. CHEMICAL COMPOSITIONS

In addition to those elements which may be considered

the main components of an alloy, modern metallurgy is most

intimately involved with the effects of minute amounts of

other elements. These may be impurities inherited from the raw materials or they may be picked up from furnace linings,

crucibles, etc. In any event, most contaminants are deleterious to the final alloy. However, trace quantities

of some elements, not normally impurities, may be added

deliberately to enhance the alloy performance.

Of further concern to the chemical composition requirements with respect to trace elements is the fact that the

material sources and the processing methods may vary

appreciably among the producers for a particular alloy. As

a consequence, each may have his particular problems with

respect to control of these elements. Thus the compilation

5
of essential plus desired elements into a prospective table

of composition for most standards is somewhat akin to a roll

call of an appreciable segment of the periodic table.

The results of a survey conducted in 1950 by ASTM

Committee E-2 on Emission Spectroscopy revealed that at that

time 13 elements were required for inclusion in proposed

cast iron spectrochemical standards. Also significant was

the realization that eight individual standards would be

required to cover the wide ranges of concentration for most

of the desired elements. In 1955 ihe NBS, in cooperation

with the cast iron industry, planned the chemical compositions for eight white cast iron spectrochemical standards.

The final compositions adopted by NBS and accepted by

industry are shown in table 1. As can be seen,, the proposed

standards were planned to contain a concentration range for

21 elements (and iron) . To provide for general application

of the standards., five commercial cast iron compositions

were chosen: piston ring, wear plate, die, brake drum, and

mold. To these, three special compositions were added to provide for the required wide concentration ranges of the

contained elements.

The balancing of the eight compositions to promote a white structure required careful study [2]. For example,

the silicon content is the principal factor in controlling

depth of chill. Chromium and vanadium are strong carbide

formers and hence markedly promote the chilling properties.

6
Table 1. Planned Compositions of Eight Proposed

NBS White Cast Iron Spectrochemical Standards

Number

Designation

1 2 3 4 5 6 7 8 Piston

Ring

Wear

Plate Die

Brake

Drum Mold

Modified

A B C Element % * % % Jo %

C 3-8 2-5 3-0 3-3 3-4 4.0 2.0 3.1

Mn 0.6 0-3 0.9 0-75 1.2 1-5 0.5 1.0

P .4 .6 . l • 2 0.05 0-3 .8 0.01

S •07 .04 .02 .2 .1 .05 • 03 .02

Si 2.8 •9 1.9 1-5 3-2 2-7 .5 2.0

Cu 0-7 •05 0. 15 0.4 0.2 1-5 .5 1.0

Ni .05 3-0 2.2 1-3 .03 0.1 .2 0.5

Cr •5 1.4 0.8 0.2 .1 2.0 •03 .08

V .15 0.005 .02 •03 •25 0.1 •05 • 07

Mo .6 1-5 •9 •3 •15 • 03 .01 .02

Ti .2 0.1 •15 .02 •35 .002 • 01 .005

As .005 .01 .02 •05 •07 .1 •15 .2 Sb •3 .2 .1 .1 •05 .02 .01 .005

Sn .005 .02 .07 .1 .02 .04 .01 •15 Co .005 • 1 •05 .02 •03 .015 .005 .01 Te .02 .01 .005 •03 •05 .06 .005 .025

B •002 • 02 .1 .05 .0007 .001 .01 .005

Bi .02 .03 .04 .005 .01 . 005 . 02R . OR

Pb a .005 .01 .002 .02 .005 .02 Zr .04 .02 .005 .1 .01 •15

Al

a Dashes indicate that no addition for this element was planned. For aluminum it was anticipated that a concentration

range of about 0.01 to 0.1 percent would be obtained as a result of this element being present in several of the planned

master alloy additions.

7

730-267 0-64—

3
Phosphorus and nickel reduce the depth of chill. Manganese

and sulfur usually form manganese sulfide., and if balanced

with respect to each other in the proportions added, have

little effect on the chill. In the absence of enough

manganese, however, sulfur has a marked stabilizing action

on the cementite and promotes chill.

In the cast iron industry, the tendency to graphitize

often is expressed as the "carbon equivalent", an empirical

relationship of the total carbon, silicon, and phosphorus

content expressed by the formula: CE = $TC + 0.3 ($Si + %P) . Most gray iron foundries prefer to hold their CE within the

range of 3.9 to 4.3. When the eight planned compositions are examined in the light of their carbon equivalents, as shown

below, it is evident that on this basis, several of the

Carbon Equivalents

Number 122^5.678

Value 4.9 3.0 3.7 3.9 4.5 5.0 2.4 3.8

compositions have considerable tendency toward graphitizing

.

Admittedly, this crude calculation does not take into account

the other elements present in the proposed standards; however, it appeared desirable to add the powerful carbide

stabilizers, tellurium and bismuth, to ensure heavy chilling

and also to provide a concentration range for these elements

as well

.
5 . CASTING

Early attempts to prepare white cast iron standards

included: centrifugally-cast pins (Research Laboratories of

the General Motors Corp.), machine-cast bolts and centrifugallycast large diameter pipe (American Cast Iron Pipe Co . )

, and

unidirectionally solidified slabs cast on a copper plate

(Watertown Arsenal) . Although none of these were entirely

successful, the results of studies at NBS on the cast slabs

appeared promising; it was determined that (l) a suitable

depth of chill for standards could be induced for most cast

iron compositions; (2) homogeneity of both composition and

structure were satisfactory , particularly near the chillcast surfaces; and (3) samples cut from the slabs were

equally suitable to both optical emission and x-ray spectrochemical methods of analysis. Because of the extreme hardness (RC > 60) of the white cast irons, however, cutting the

slabs to samples was found not to be economically feasible.

As a consequence of the work on the unidirectionally

cast slabs, a massive water-cooled copper mold assembly was designed and constructed at NBS for unidirectional casting

of a large number of white cast iron samples simultaneously.

The mold assembly, shown in figure 1, consists of a 5-ft square steel plate to the periphery of which was edgewelded a 5-in. wide steel strip to form a 5-ft annulus having

a tangential outlet. Within this area another strip was edge

welded to serve as a spiral baffle from center to periphery

9
Figure 1. Water-cooled copper mold assembly designed

and constructed at NBS for the preparation

of white cast iron spectrochemical standards

.

for water cooling. To the top of this structure was bolted

a 5-ft square copper plate, 1-in. thick. The copper plate

was made from oxygen-free, high conductivity (OFHC) copper.

The bolts, 1 in. in diameter, also were made of OFHC copper

and were threaded to extend into the copper plate about twothirds of the thickness. A lead gasket near the periphery

sealed the entire assembly to prevent water leaks.

10
The cooling water was supplied by a 2-in. hose line

connecting the high-pressure line to the plate center; the

3-in. exit line was equipped with a valve to serve in a throttling capacity to aid in purging air from the cooling

chamber

As the result of a number of experiments with different

kinds of mold wash, it was found that the best protection to the copper plate consistent with high heat transfer and least

moisture difficulties was accomplished by dressing the casting surface with a very thin layer of colloidal graphite with

alcohol as the carrier. The casting face was flame dried

until the time of casting.

To facilitate gang-casting of the white iron samples,

a grid mold assembly was mounted on top of the copper plate.

Each grid mold, nine total, consisted of a three-part, pasted

up and baked sand assembly (18 x 18 in. sq) which would accom- modate 64 white iron blocks each separated by about 1/4 in. at the chill face. Surmounting the grid was a plate, 3/4 in.

thick, having a tapered in-gate located over the center of

each block cavity in the grid. The size of the in-gate was found critical in that too small an opening fostered lack of

fill, cold-shuts, and spatter, while too large an opening

risked damage to the cast white-iron block during subsequent

break-off from its header. Good castings were obtained with

in-gates having 1/2- to 5/8- in. diameter at the block

cavity, and a 1/8-in. taper.

11
The top section of the mold consisted of a rim which

formed a basin 1 7/8-in. deep above the in-gate plate, and

which had a cut-out on those sides which contacted other

grids to permit interflow of metal after the metal had filled the cavities , the in-gates, and to a depth of 1/4 in. in

the basin.

The final casting procedure adopted may be characterized

as a stoppered tun-dish technique. Essentially this consisted of providing at the top of the entire mold assembly a rammed pouring basin having stoppered holes, 2 in. diameter,

one over each of the nine grid basins . Each grid basin was covered except for the stoppered opening. In the casting

operation more than enough metal to fill the entire mold was poured in the basin, following which all stoppers were pulled

simultaneously

.

Since each grid mold accommodated 64 blocks and nine

such grids were available, the casting procedure had the

capability of producing 576 white cast iron samples simultane

ously. However, the 10 positions at the outside four corners

of the assembly were blocked off since these positions were

not directly above the spiral of the water cooling. This re- sulted in a production capacity of 536 samples per heat.

12
6. MELTING

Experimental melting at NBS was carried out in a highfrequency induction furnace of 1000-lb rated capacity; however 3 all production heats were made at the Naval Research

Laboratory in a similar type furnace but with 350-lb rated

capacity

.

A listing of the materials used in melting the eight NBS

white cast iron standards is given in table 2. With the ex- ceptions of the materials for sulfur, antimony, tellurium,

and bismuth, considerable experience had been gained with the

listed materials previously in the preparation of eight NBS

ingot iron and low-alloy steel spectrochemical standards [3].

Careful control was maintained over the melting procedures to include time, temperature, and amount and order of

additions to the furnace. Table 3 shows as an example the

melt log for the white cast iron brake drum standard (No. 4

in Table 1, NBS No. 1179). The total melt time for each heat

was about 1 1/2 hours. In general, the expected and calculated

recoveries for the elements agreed well. Table 4 illustrates

the recoveries obtained for 10 of the 20 elements added. For

vanadium, the high average recovery value possibly was due to

The authors express their appreciation to L. Depue and the

foundry staff at the Naval Research Laboratory both for their

suggestions in the final development of the casting procedure

and for permitting the use of their facilities and personnel

in the production of the eight NBS cast iron spectrochemical

standards

.

13
Table 2. Materials Used in Melting NBS

White Cast Iron Standards

Element Material Des cription Purity a

C b Electrode grade, rods 3-in. diam. onyy o_i_^

• y+

Mn Electrolytic, platelets OV9 ( +

p FeP, lump (24$ P) 99

S FeS, lump (36.5$ S) 99

Si b Metal , lump 97 + Cu OFHC, rod ends 99 9 Ni Electrolytic, small plates 99 9 (Ni + Co)

Or Metal , lump 97 +

V FeV, lump (48.8$ v) aft rr5 Mo Metal , wire 99 +

Ti FeTi, lump (40.0$ Ti) 3o 5 AS Metal , lump QQyy +

OkDO Metal , lump oo

yy +

on Metal , small ingot ooyy

o uo Metal y pellets oo

yy +

Te CuTe, lump (45.5$ Te) ooyy +

B FeB , small lump (11-5$ B) 98 5 Bi Metal 5 small lump 99 5+

Pb Metal , shot 99 + Zr SiZr, small lump (41.3$ Zr) 99 +

Fe b Ingot iron, plate squares 99 8+ c

a Semiquantitative spect rochemical analyses were obtained on

all materials to ensure positive identification and to determine the approximate concentrations of the impurities

that could affect the schedule for additions

.

b A master alloy of carbon, silicon and iron was prepared and

used for the main additions of carbon and silicon. Chemical

determinations showed 2.56$ C and 2.72$ Si.

c Quantitative chemical and spectrochemical determinations

were made for 20 elements in the ingot iron.' By difference,

the iron content was 99.85$.
Table 3. Log of Melt for Brake Drum (350 lb)

Standard (NBS No. 1179) January 8, i960

Charge: Master Alloy melting stock (305-23 lb), Ni (4.50

lb), Cu (1.0 0 lb).

Furnace On : 9:30 AM. Half Melt Down : Time 10:15 AM; added C (1.88 lb), Si (none),

Mn (2.68 lb)

.

Melt Down : Time 10:43 AM, Temp. 2500°F

.

Skim : Time 10:45 AM, Temp, at end 2475°F

.

Additions : (Non-volatile) Temperature to 2500°F, Time 10:46

AM, P(2.78 lb), S(1.92 lb), Cr(0.70 lb), Mo(l.05

lb), V(0.22 lb), Co(0.07 lb), Ti(0.44 lb), Zr

(0.18 lb), Time: 10:48 AM, Temp. 2520°F.

Stir : Time 10:52, Temp. 2550°F.

Skim : Time 10:53, Temp. 2500°F

.

Additions : (Volatile) Temperature to 2500°F, Time 10:54 AM

As (0.17 lb], Sb(0.39 lb), Sn(0.39 lb). B(1.79

lb), Pb(0.88 lb), Te(0.26 lb), Bi(0.019 lb).

Stir : Temperature to 2600°F rapidly. Time 10:58 AM. Tap : Stir in ladle Time 10:59 AM. Mold Water on : Sample : Two specimens

Pour: Time: 11:00 AM

Remarks

No apparent spattering of additions. 555 of 556 casting

blocks filled.

15
Table 4. Recovery Values for 10 Elements in

the Eight NBS White Cast Iron Standards

Average Recovery Values

Concentration

Element Range- Expected Obtained

JO % %

C 2.0 to 4.0 90 88

Mn 0.3 to 1.5 95 95

p .05 to 0.8 100 99

S .03 to .2 8o 68

Si • 5 to 3.2 95 90

Cu .2 to 1.5 100 101

Ni .1 to 3.0 100 100

Cr .08 to 2.0 100 100

V .02 to 0.25 100 103

Mo .15 to 1.5 100 100

a small error in the assignment of the vanadium content in the

f errovanadium used.

7. PRELIMINARY ANALYSIS

Prior to pouring the molten metal into the mold, two ladle samples to serve for preliminary analysis were obtained

by casting into separate containers mounted on the copper

plate. These samples were designed to be similar to the cast standard samples in size and shape. One of these samples was fractured and examined rapidly before casting the main heat

to determine whether the white iron structure was obtained

throughout the casting thickness. Had the test sample for

any of the heats exhibited evidence of free rather than

16
combined carbon, a further addition of tellurium to the

molten metal in the ladle was planned.

The sample which had been fractured was retained at NBS

for preliminary analysis; the second sample was sent to a cooperator* for preliminary analysis and for application

evaluation by comparison with their analyzed spectrochemical

cast iron samples.

With the exceptions of carbon, phosphorus, and sulfur,

which were determined chemically, spectrochemical analysis by

both optical emission and x-ray served for all other

determinations

.

Complete analysis for each heat was obtained before

preparing a subsequent heat to adjust the recovery values and

to ensure adequate coverage of the required concentration

ranges for the added elements.

8. HOMOGENEITY TESTING

A large amount of homogeneity testing was deemed

necessary because of the new casting procedure and because of

the complexity of metallurgical structure-- In the white iron

samples. At NBS, this testing was accomplished primarily by

x-ray spectrochemical analysis ; however, optical emission and

chemical methods of analysis also were employed, as well as metallographic examinations. In addition, four cooperating

laboratories provided major contributions toward the

,

W. R. Kennedy, American Cast Iron Pipe Co., Birmingham, Ala.

*-* Spectrochemical Analysis Section, National Bureau of

Standards, Washington, D. C. (D . M . Bouchette, Jr.)

17
homogeneity testing

For each standard,, several samples were chosen to test for variations in composition and structure: (1) from bottom

to top and from inside to outside of the individual samples;

(2) among samples from different locations in the same grid

mold; and (3) among samples from each of the nine grid molds.

As a result of detailed metallographic studies and in

combination with homogeneity testing of composition, it was determined that the full sample thickness of in. was not sufficiently uniform and the decision was made to certify

only the bottom half of the samples. When this was done, the

variations in structure and composition were found to be

within limits adopted for certification.

In the metallographic examination, samples from each of

the eight prepared white irons showed near the chill cast surface a columnar type of structure which extended upward

approximately one-half the sample thickness; above this the

structure consisted of randomly oriented dendrites. The

change to random orientation was gradual in samples of NBS

Nos . 1178 and 1180, with no distinct boundary between the two types of structures as was true for the other white irons.

American Cast Iron Pipe Co., Birmingham, Ala.

(¥. R. Kennedy)

Chicago Spectro Service Laboratory, Inc., Chicago, 111.

(A. Goldblatt)

General Motors Corporation, Research Laboratories,

Warren, Mich. (M. D. Cooper)

International Harvester Co., Manufacturing Research,

Chicago, 111. (M. E. McKinney)

18

I
Table 5 shows some typical x-ray results of homogeneity

testing for manganese , nickel and molybdenum in the brake

drum standard^ NBS No. 1179. Similar test data were obtained

for each of the 20 elements contained in the eight white iron

standards

.

To make the standards available for issue at the earliest

possible date, it was planned to provide initial certification

for only the first 10 elements shown in table 1. Following

evaluation of the homogeneity test data, the 10 elements were

found to have acceptable homogeneity in all eight standards.

In several instances, the results of the statistical

evaluation (table 5) indicated definite inhomogeneity; the

amount, however, was small and was deemed acceptable from the

practical standpoint. The criterion adopted for statistical

significance of inhomogeneity was "that the total difference

between the two main items for contrast must exceed three times

the test level. The test level is the standard deviation of

the reported average which is obtained by dividing the

calculated standard deviation by the square root of the

number of values on which the average is based.

Providing that the analytical method of testing provides

high precision, such as shown for the "within plate" testing

for molybdenum, and depending on the number of replications,

it is frequently possible to observe statistical significance

for inhomogeneity. The "within plate" test level for

molybdenum is only 0.000 2 percent; thus a difference between

19
Table 5. Typical Homogeneity Test Data: Manganese.,

Nickel , and Molybdenum in Brake Drum Standard,

NBS No. 1179. by X-Ray Determinations.

Test

Within Sample

JjOTjTjOm, /o ^iiV . Ol Lt

J 0.642-3 -L O^O, 0.3259

Center, % (Av. or 4] r )i -z .6437 1.35i

Difference, $ .OOI4 0 .002 .000 2 Difference from mean, % . UUU7 . UUl . uuu^

% Difference from mean .11 .07 .03 *Test level, % .ooi8

.oo 2 .ooi4 Significance

Statistical no no no

Ptq /^i—1 r* a ~l JTI clL- OlLdl no no no Within Plate

Center, % (Av. of 8) 0.645s 1.33s 0.3277

"Frirrp ^ ( Av nf P>) . 64o 2

-L1 • ^60

Ti-i iJiiff1 prpnfp ci ciiL c ^ yo . ^^S>0 0 0?)i Difference from mean, % .0028 .oi 2 .OOI7

% Difference from mean .44 .89 .52 Test level, % .0030 .oo 2 .ooo 2 Significance

Statistical no yes yes

Practical no no no Among Nine Plates

Maximum, % (Av.. of 4) 0.3277 Minimum, % (Av. of 4) 636x 1 34^

Difference, % 017^ 0 0l£ 002o

Difference from mean, % .0085 •008 .OOI4

% Difference from mean 1.52

" .59 o43 Test level, % .oo4 P .00n .000h

Significance

Statistical yes yes yes

Practical no no no

Test level: standard deviation of the reported average.

20
"center" and "edge" as small as 0.0006 percent would appear

statistically significant. At the concentration level of

about 0.5 percent for molybdenum, such a small difference

has little practicality. If it is assumed that certification

will be to the nearest 0.01 percent., the actual difference

found of 0.003^ percent (+ 0.001^ percent from the mean) also

has no practical significance. Practical significance is

adjudged on the basis of (1) method precision, (2) number

of replications in testing, (5) the concentration of the

element under test, and (4) the accuracy of the certification

(which may itself, in some instances, be limited by the

homogeneity). For the concentration range of about 0.1 to

5 percent, a variation of approximately of + 1 percent of the

amount present is normally acceptable, whether or not

statistical significance is observed. The value of + 1.5

percent for manganese among the nine plates was deemed

acceptable from the practical standpoint although falling

somewhat outside of the ± 1 percent criterion.

9. SAMPLE IDENTIFICATION

Since only half of the sample was found of suitable

homogeneity, it was important that positive identification

of the certified portion be made known. Figure 2 shows a schematic diagram of the NBS white cast iron spectrometric

samples. As can be seen, the samples have been numbered on

the face opposite to the chill cast surface.

21
SCHEMATIC DIAGRAM OF

NBS WHITE CAST IRON SPECTROMETRIC SAMPLES

1^2 MACHINE GROUND FROM EACH OF FOUR SIDES

Figure 2. Schematic diagram of NBS white cast iron

spectrometric samples.

The samples were cast with a taper to the sides. This

offers positive and permanent identification of the certified

portion of each sample "by noting that the test face always

will be the largest surface. The exact certified portion is

that extending upward 5/l6 in. from the test surface of the

sample as received. Only this portion was analyzed in the

cooperative program for certification.

Because of the extreme hardness of the white cast irons,

it was necessary to number the samples by abrasion with

22
carborundum dust blown through a template under high air

pressure. Since the indentation is shallow, care will be

required in the laboratory to maintain identities. A further

complication is the fact that the white iron samples are subject to rather severe rusting.

10. HEAT TREATMENT

The high susceptibility of the cast samples to cracking

during the final processing operations posed a serious problem

not only for the original sample preparation at NBS, but also

to the ultimate user. As a consequence, it was essential to study the stress relief heat treatment of these drastically

chilled castings to arrive at a compromise that would permit

a reasonable amount of careful grinding and yet not cause enough metallurgical change in the material to initiate

graphite precipitation [4],

A series of stress relief heat treatments over the

temperature range of 370 to 8l5°C (700 to 1500°F) for one hour were given to samples from each of the eight standards.

By metallographic examination, the presence of a graphite or carbon precipitate could not, in some instances, be definitely

determined; however, graphite was definitely present in most

samples having received the 8l5°C (1500°F) treatment. None

of the specimens treated at 595°C (1100°F) showed graphite

precipitation. Moreover, samples treated at this temperature

were found to be free from cracking during sectioning, grinding,

or polishing. As the result of these tests, all samples were

23
given the selected heat treatment of one hour at 595°C . It

is important to note, however, that the samples are still

sensitive to cracking by careless cutting or grinding.

11. CHEMICAL ANALYSIS

Samples for cooperative chemical analysis for certification were obtained by breaking brittle segments, cut from

the certified portion of representative samples, in an iron

mortar with an iron pestle. Chemical analyses were made at NBS and in five cooperating laboratories*. Provisional

Certificates of Analyses were prepared in April, 1961 and the

samples released for issue; the values appearing on the

Certificate for the 10 elements in the eight standards are shown in table 6**. By comparing these values with those for

the planned compositions (table 1), it is clear that close ~¥ Quantitative Separations Section (formerly Standard

Reference Materials Section), National Bureau of

Standards, Washington, D. C. (J. I. Shultz and

June Maienthal)

.

American Cast Iron Pipe Co., Birmingham, Ala. (R. Elder

and R. Deas )

.

Research Laboratories, General Motors Corp., Warren, Mich.

(R. B. Loranger )

.

Naval Research Laboratory, Washington, D. C. (D. Walter

and Ove Mylting)

.

Rolland Machine Works, U. S. Steel Corp., Canton, Ohio

(D. J. Henderson).

Applied Research Laboraotry, U. S. Steel Corp.,

Monroeville, Pa. (L. M. Melnick)

.

A brief summary of the chemical methods used to determine

each of the 10 elements, together with a listing of the

cooperative results, is available on request to the Analytical

Chemistry Division, National Bureau of Standards,

Washington, D. C. 24
Table 6. Provisional Certified Values for Eight NBS

White Cast Iron Spectrochemical Standards

(April 1961)

NBS No. Design a ~f~ 1 piTi

1176 1177 1178 1179 1180 1181 1182 1183

Piston

Rins

Wear

Plate Die

Brake

Drum Mold

Modified

A B C Element % % % % % % %

C 3.47 2.74 3.11 3.35 3.28 a 3.63 1.97 3.05

Mn 0.63 0.37 0.86 0.64 1.12 1.32 D.45 0.91

P .42 .61 .115 .23 0.055 0.29 .85 .011

S .061 .037 .026 .165 .086 .052 .046 .025

Si 3.19 .88 1.91 1.35 3.04 2 .54 .31 1.70

Cu O.76 ,087 0.16 0.4l 0.20 1.47 .49 1.01

Ni .055 2.97 2.25 1.31 .044 0.11 .22 0.53

Cr .51 lo39 0.89 0.23 .14 2.04 .029 .077

V .17 0 o 005 .017 .036 .26 0.11 .060 .080

Mo .59 1.49 .94 .31 .155 .042 .018 .029

a This standard contains some free graphite (approximately

0.1 percent; the other standards contain less than 0.01

percent )

.

agreement for most was obtained.

Current plans are to certify additional elements in

these standards as well as in new cast iron standards.

12. CONSISTENCY TESTING

Following completion of the analytical program for

certification^ but prior to issue of the standards., a consistency test was performed. In this test, applications

of the standards in both optical emission and x-ray methods

25
were investigated. The standards should provide points which

fit smooth analytical calibration curves when compared as a set and when compared with other reliable standards.

Several sets of individual company standards (not

generally available) were provided to NBS on a loan basis.

Good agreement was observed among the eight NBS standards and

among the sets of standards for the elements manganese, silicon,

copper, nickel, chromium, vanadium, and molybdenum. For

carbon, a bias was exhibited between different sets when

examined with vacuum optical emission spectrometers by

outside cooperating laboratories . It was determined that

the degree of chill was critical for the carbon determination.

This finding serves to emphasize the important requirement

that samples for analysis and standard samples must be closely

matched with respect to all variables, such as size, shape,

composition, and metallurgical condition. Any departure

from this principle must be investigated thoroughly to ensure

that a bias has not been introduced.

Whereas the results of the consistency testing

demonstrated that the NBS standards can be used directly in

the laboratory for the analysis of white iron samples for

elements other than carbon, local re-evaluation or the

preparation of additional reference samples may be required

for the carbon determination by spectrochemical means. __

Applied Research Laboratories, Dearborn, Mich.

Hilger and Watts, Ltd., London, England

Motor Castings Co., Milwaukee, Wise.

26
13. PRECAUTIONS FOR APPLICATION

Several precautions need to Toe taken in the application

of these standards to spectrochemical analysis. The surface

preparation for x-ray spectrochemical analysis was found to

"be critical since the samples exhibited metallurgical

structure changes not only among the standards , but also from

bottom to top of the certified portion of each sample. It is

known j for example s that careful surface preparation normally

is required for the determination of the light elements , those below atomic number 22. This is because nearly all of

the emitted secondary radiation from the sample is absorbed

except for that emanating from the immediate surface. A

metallographic polishing technique has proven to be the

ultimate in surface preparation for solid metallic samples

[5]. This minimizes the effects of differences in structure

as affected by surface preparation,, and the effects of tearing

or smearing of the surface of samples for analysis. For

application of the standards to x-ray analysis s each

laboratory will need to ascertain the surface preparation

necessary to minimize apparent differences in composition not

only among the standards ^ but also between standards and

samples for analysis as well.

Although the change in structure may influence the

results of optical emission analysis s depending on the

excitation and exposure conditions^ this generally was not

27
found to be a serious problem. Apparent differences in

composition were observed in optical emission analysis

,

however, from center to outside of a sample rather than from

bottom to top as was exhibited by x-ray. To confirm this

finding, the x-ray beam was masked to provide an irradiated

area on the sample about the same size as the optical emission

burn. The same testing was performed, but no significant

differences in composition were observed. On further

investigation, the apparent differences exhibited by optical

emission were attributed to a differential heating effect.

The heat conductivity of the white iron samples was found to be poor. In effect, just the sparked surface and

the immediate adjacent area became hot, not the entire

sample as was true for copper or steel. Thus differences in

volatility rates for some elements occurred with the white

iron samples and these were dependent on the location of the area sparked. Near the edge of the sample the heat was dissipated more rapidly to the atmosphere in contrast to center positions where the heat dissipation was restricted

largely by the poor conductivity of the metal. To obtain

the most reliable optical emission results, then, each

laboratory should closely match standards and samples for

analysis not only with respect to size and shape, but also

with respect to the position of sparking.

28
Although not believed to be critical in application, it

should be noted that NBS Standard No. Il80 was found to contain approximately 0.1 percent of free graphite; the other

standards all were found to contain less than 0.01 percent.

14 . ADDENDUM

Two new white cast iron standards , a high- and a lowcomposition alloy , were melted and cast in February, 1964.

These standards were required in view of the limited supply of

eight standards prepared previously and they are designed to serve the long-term need for this type of standard. Homogeneity

testing is now underway and if satisfactory the standards will

be certified initially for Ti, As ; Sb, Sn, Co, Te, B, Bl s Pb,

Zr, and Al

The two new white cast iron standards were also prepared

at the Naval Research Laboratory, using procedures similar to those described previously except that a double quantity was melted and two gang castings were made for each heat. Nonvolatile elements were added to the initial melt, one half of

which was then tapped into a ladle and poured into a holding

furnace. The volatile elements were added to the melt in the

original furnace and the first gang casting completed on the

water-cooled copper plate. After preparing a second mold

assembly, which required less than one-half hour, the holding

furnace was brought to temperature, identical quantities of the

volatile elements added, and the second gang casting completed.

29
Since small differences in composition will undoubtedly

exist between the first and second gang casting for each

standard^ the second casting in each case will be treated as

a separate standard. It will be issued as a renewal standard

when the quantity of the first casting has been exhausted^

although it will be tested and analyzed simultaneously with

the first casting.

A narrated^ color,, motion picture showing the melting

and casting of the new NBS white cast iron standards is being

prepared under the direction of the Naval Research Laboratory

personnel. The National Bureau of Standards will have a copy

available for loan by fall of 1964.

30
15. References

Michaelis, R. E. , Yakowitz, H. , Moore, G. A., Metallographic characterization of an NBS spec trome trie low

alloy steel standard, J. Res. NBS 68A (Phys. and Chem.),

No. 4 (July Aug. 1964). (in press).

ASTM Committee on Chilled and White Cast Irons, Metals

Handbook, 8th Ed. 1, 394 (l96l).

Michaelis, R. E., Preparation of alloys for spectrographic

standards (1956). Unpublished NBS report.

Wyman, L. L., Park, J. J., Development of NBS Spectrographic standard samples for iron and steel, 1954-1955

(i960). Unpublished NBS report.

Michaelis, R. E., Kilday, Betty Ann, Surface preparation

of solid metallic samples for X-ray spectrochemical

analysis; Book, Advances in X-ray Analysis 5, 405-411

(Plenum Press, Inc., New York, N. Y., 1962)

.

31

GOVERNMENT PRINTING OFFICE : 1964 0 — 730-267

Announcement of New Publications on Standard Reference Materials

Superintendent of Documents

Government Printing Office

Washington, D. C. 20402

Dear Sir: Please add my name to the announcement list of new

publications to be issued in the series: NBS Miscellaneous

Publication 260 - Standard Reference Materials.

Name

Company

Address

City State Zip Code

(Notification key N-330)